The Steam platform is the largest digital distribution platform for PC gaming, estimated in 2013 to have 75% of the market space.[4] By 2017, users purchasing games through Steam totaled roughly US$4.3 billion, representing at least 18% of global PC game sales.[5] By 2019, the service had over a billion registered accounts with 90 million monthly active users. The success of the Steam platform has led to the development of a line of Steam Machinemicroconsoles, which include the SteamOSoperating system and Steam Controllers, and the Steam VR platform.

Before implementing Steam, Valve Corporation had problems updating its online games, such as Counter-Strike; providing patches would result in most of the online user base disconnecting for several days. Valve decided to create a platform that would update games automatically and implement stronger anti-piracy and anti-cheat measures. Through user polls at the time of its announcement in 2002, Valve also recognized that at least 75% of their users had access to high-speed Internet connections, which would grow only with planned Internet expansion in the following years, and recognized that they could deliver game content faster to players than through retail channels.[6] Valve approached several companies, including Microsoft, Yahoo!, and RealNetworks to build a client with these features, but were declined.[7]

Between 80,000 and 300,000 players participated in the beta test before the client's official release on September 12, 2003.[13][14][8][15] The client and website choked under the strain of thousands of users simultaneously attempting to play the game.[16] At the time, Steam's primary function was streamlining the patch process common in online computer games, and was an optional component for all other games. In 2004, the World Opponent Network was shut down and replaced by Steam, with any online features of games that required it ceasing to work unless they converted over to Steam.[17]

Valve's Half-Life 2 was the first game to require installation of the Steam client to play, even for retail copies. This decision was met with concerns about software ownership, software requirements, and issues with overloaded servers demonstrated previously by the Counter-Strike rollout.[18] During this time users faced multiple issues attempting to play the game.[8][19][20]

Beginning in 2005, Valve began negotiating contracts with several third-party publishers to release their products, such as Rag Doll Kung Fu and Darwinia, on Steam.[21] Valve announced that Steam had become profitable because of some highly successful Valve games.[22] Although digital distribution could not yet match retail volume, profit margins for Valve and developers were far larger on Steam.[23] Larger publishers, such as id Software,[24]Eidos Interactive,[25] and Capcom,[26] began distributing their games on Steam in 2007. By May of that year, 13 million accounts had been created on the service, and 150 games were for sale on the platform.[27][28] By 2014, total annual game sales on Steam were estimated at around $1.5 billion.[29]